DESCRIPTION: Acute respiratory infection is now the leading cause of mortality in young children under 5 years of age, accounting for nearly one fifth (20%) of childhood deaths worldwide. Human parainfluenza viruses (HPIVs) and respiratory syncytial virus (RSV) are paramyxoviruses that cause the majority of childhood croup, bronchiolitis and pneumonia in the U.S. Despite the impact of these diseases on illness and hospitalization of young infants worldwide, no drugs or vaccines are available. With this application, we are poised to develop a new broad-spectrum antiviral strategy based on inhibiting fusion during viral entry. We found that lipid-conjugated peptides derived from the fusion protein of HPIV3 block fusion intermediates during viral entry and inhibit both HPIV and RSV infection. By combining structure-based optimization of fusion inhibitors, backbone modification to enhance half-life, and modification of lipid components with virologic and in vivo assays, we aim to identify and characterize novel HPIV3/RSV fusion inhibitors that can be administered intranasally and have significantly improved antiviral efficacy. Bio distribution studies in animals show that a single intranasal administration of our lead HPIV3 peptide inhibitor generates adequate antiviral concentrations in the lung. We will exploit the uniquely broad antiviral activity of our prototype HPIV3 derived peptides to test our hypothesis that lipid linkage combined with peptide backbone modification can deliver potent antiviral agents. We plan to determine the optimal dose regimens and routes of delivery, and to develop a useful, easily deliverable, short-term acting antiviral product. By combining the two recent innovations -- membrane targeting and backbone modification -- we aim to generate effective anti-HPIV/RSV inhibitors for human disease, via the following two Specific Aims. Aim 1. Identify and develop optimized membrane-targeted anti-HPIV3 and anti-RSV broad spectrum peptide inhibitors. We will combine conventional peptide design (? residue side chain modification) with backbone-modification (?? replacement) and lipid-based membrane targeting to optimize fusion inhibition activity. These efforts will be guided by biophysical and cell-based measurements. Aim 2. Effectiveness of broad spectrum membrane-targeted C-peptide inhibitors to protect against respiratory infection in animal models of human HPIV3 and RSV infection. Challenge experiments in cotton rats - an ideal small animal model for both HPIV3 and RSV infection - will determine the required dose for therapeutic efficacy, and the therapeutic time window. We propose that backbone modification and membrane targeting strategies may be synergistic, and that their combination will generate antiviral agents that can be delivered intranasally with unprecedented efficacy and pharmacokinetic properties. Iterative cycling among design efforts and in vitro and in vivo studies should lead to promising investigational anti-HPIV/RSV agents.